1. Field of the Art
The present invention relates to a water lubricated bearing or water lubricated seal which has high wear resistance and a low coefficient of friction, and more particularly to a water lubricated bearing or water lubricated seal which is suitable for use in fluid machinery, e.g., pumps, turbines, compressors, etc.
2. Prior Art
Many conventional water lubricated bearings or water lubricated seals which have heretofore been used for fluid machinery, e.g., pumps, turbines, compressors, etc., have an arrangement comprising a combination of a movable member which employs a ceramic material such as SiC as a substrate, and a stationary member which employs a hard metal such as tungsten carbide (WC) as a substrate.
With the need for fluid machinery to be reduced in size, operate at higher speed and increase in capacity, service conditions under which seals and bearings are used have become increasingly adverse in recent years. That is, seals and bearings are now used under high-speed and heavy-load conditions. Accordingly, it has been pointed out that a material such as a hard metal which has heretofore been used for seals and bearings gives rise to problems such as fracturing under thermal shock and thermal fatigue cracking, caused by repeated application of friction heat generated by sliding contact between solids.
On the other hand, ceramic materials, e.g., SiC, are superior to hard metals in resistance to thermal stress caused by sliding. However, when used as a material for a high-speed rotating member, a ceramic material is inferior in mechanical strength and lacks resistance to shock. Further, when a metallic material is used as a sliding member, the surface of the metallic material may be subjected to carburizing, nitrating or other similar hardening treatment. With these surface treatments, however, a satisfactory sliding surface cannot be obtained in terms of the hardness of the modified layer itself and the deformation of the substrate after the treatment.
In addition, in a conventional water lubricated bearing or water lubricated seal adopting a titanium nitride film coated on a substrate of a metallic material, since an appropriate material for mating with the titanium nitride film has not been provided, sufficient sliding characteristics in water could not been obtained.